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How Big Do Rainbow Trout Get? (Plus More Interesting Facts)

how big do rainbow trout get

How Big Do Rainbow Trout Get?

Rainbow trout, one of the most popular sport fish in the states today. From urban ponds, to mountain streams. Big rivers to coastal coves, the rainbow trout is now stocked for recreational purposes all around. Though native to only the Pacific Northwest, rainbow trout has gained popularity as a sport fish and hatchery fish worldwide.

Most fishing outings generally yield rainbow trout from 10 inches to 16 inches long. Most will average under 2 pounds. However, rainbow trout are known to bulk up and be some of the hardest fighting trout out there.

Whether it is a productive high mountain lake, or a large clear river in the Pacific Northwest, rainbow trout have the potential to pack on the pounds and become a serious trophy.

Factors That Affect A Trouts Size

Generally, most fish are considered to have indeterminate growth. This means that unlike humans, fish can continue to grow in size for the duration of their lives. The only limiting factor to finding giant fish is generally age. However, there are other factors that influence the potential size a fish can achieve. Some of these factors include:

  • Genetics
  • Available food
  • Overall size of the environment.


Generally speaking, the size of the environment and the available food sources have the most influence on trout getting to those trophy sizes. Don’t expect to find a 20 plus inch rainbow in a small mountain stream, though it is always a possibility.

Instead, if you are fishing for big rainbows, try to fish a water body that is larger. Such as a larger creek, river, lake, or reservoir. Here, the environment is more conducive to growing larger fish.

Local Food Source

Additionally, the available food sources are a big factor on rainbow trout packing on the pounds. Abundant high protein food sources are generally the driver of this. Freshwater shrimp, or “scuds” are known to be a practical growth supplement for trout. Lakes and rivers with an abundance of this food sources generally grow big trout.

In rarer cases, where rainbow trout key in on big high protein food sources, such as mice, they can also achieve trophy sizes. In places like Alaska or Canada, where aquatic insects can be limited in glacial streams, they have reverted to eating mice and other rodents that are swimming or fall into the water. This can lead to some exciting fishing opportunity! In situations like this, 20”+ rainbows pushing 5 pounds is fully possible!

Rainbow Trout vs. Steelhead

So what’s the deal with Steelhead? Well, Steelhead are in all technicalities the same species as a Rainbow Trout. The only thing is that their life histories and natural functions vary greatly.

While a Rainbow Trout is a freshwater fish, populations of Steelhead are simply ones that migrate back and forth to the saltwater ocean, much like a Salmon.

These trout are born in freshwater rivers and streams and spend much of their adult life feeding on the abundance of food in the oceans, returning to rivers and streams in the spring to spawn.

large steelhead caught in copper river
A large steelhead, or sea run rainbow trout (Credit: Wikipedia)

Living and feeding in the ocean produces big and healthy fish. Steelhead are known to be some of the most finicky, though most hard-fighting a fun trout to catch. The annual Steelhead runs in the spring are a big deal to a lot of people who desire to catch big fighting fish.

Steelhead on average are going to be bigger and more robust than your average Rainbow Trout, lending to their popularity. While Steelhead anglers don’t typically catch dozens of fish in a day, the ones they do land are often big submarine looking trout in the 5 to 10 pound range, a trophy by anyone’s standards.

World Record Rainbow

According to the International Game Fish Association, or IGFA, the all-tackle world-record Rainbow Trout comes in at a nearly unbelievable 48 pounds! Hailing from the famous Lake Diefenbaker, which has produced numerous record rainbow trout in the past. While this is certainly an exceptional specimen from an ideal location, Rainbow Trout are regularly caught upwards of 20 pounds throughout multiple states every year.

How do You Catch a Trophy Rainbow?

Now, catching one of these monsters is not always so simple of a task. Don’t expect to learn some secret fishing trick to catch a 10 pound Rainbow at your local lake. Chances are, it may not even exist their.

The best chance at catching nice trophy Rainbows is to go somewhere they are known to exist. A little research should lend you some locations that are known to produce these behemoths regularly. The best chance at catching a trophy rainbow, is fishing a spot other trophy rainbows are regularly caught.

Written by Don

When I'm not bass fishing or looking for steelhead in my home state of Oregon I can be found working on house projects dreaming of my next fishing adventure.

I started this website to share just some of the things I've learned along my fishing journey, and the many things I'm still learning. Enjoy!

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